6, 8-bis (hydrocarbon substituted mercapto) 5-hydroxycaprylic acids and delta-lactones thereof



United States Patent 6,8-BIS(I-IYDROCARBON SUBSTITUTED MER- CAPTO) S-HYDROXYCAPRYLIC ACIDS AND DELTA-LACTONES THEREOF Frederick W. Holly, Cranford, and Arthur F. Wagner,

Princeton, N. J., assignors to Merck & Co., Inc.,.Rahway, N. J., a corporation of New Jersey No Drawing. Application December 4, 1953 Serial No. 396,333

11 Claims. (Cl. 260343.5)

This invention relates to 6,8-dithioloctanoic acid. More particularly, this invention is concerned with novel processes and intermediates useful in the production of 6,8-dithioloctanoic acid.

In the preparation of the valuable growth stimulating substance called a-lipoic acid or 5-[3-(1,2-dithiacyclopentyl)] pentanoic acid, it has been found that this substance may be conveniently prepared by oxidation of 6,8-dithioloctanoic acid to the desired cyclic compound by procedures disclosed in the J. Am. Chem. Soc., 74, 3455 (1952). However, none of the known methods of producing 6,8-dithioloctanoic acid and related compounds are entirely suitable for this purpose because of involved procedures, low yields and the resulting high cost of production.

Therefore, an object of this invention is to provide novel processes and intermediate compounds which are particularly satisfactory for the synthetic production of 6,8-dithioloctanoic acid. Another object is to provide novel chemical compounds of use in the preparation of other valuable compounds. 7

It has now been discovered according to one embodiment of the present invention that 6,8-dithioloctanoic acid (IV) may be conveniently produced by the process which comprises reducing a 6,8-(hydrocarbon substituted mercapto)-S-oxOcaprylic acid (I) to produce a 6,8- (hydrocarbon substituted mercapto)-5-hydroxycaprylic acid which cyclizes to the corresponding B-lactone (II), reacting said lactone with a suitable reducing agent to produce a 6,8-(hydrocarbon substituted mercapto) caprylic acid (III) and subsequently converting said compound to 6,8-dithioloctanoic acid by reacting it with an agent suitable for cleaving such thioethers. may be illustrated as follows:

0 CHHCHQOH (OHz) C O OH SR SR OH [CHaCHzCHH(CH2)3C O OH] SR SR CH2 Cz CH2 CHzCHzGHlH =0 SR SR 0 II CH2CH2CH(CH2)4COOH CHrCH2CH(CH2) COOH SR SR S H SH III IV wherein R and R represent the same or difierent hydrocarbon substituents.

The first step in this process comprises reduction of the 6,8-(hydrocarbon substituted mercapto)-S-oxocaprylic acids to the corresponding S-hydroxy compounds This process Patented Sept. 23, 1958 ice and a-lactones thereof. To effect this reduction, ordinary reducing agents such as the borohydride salts including sodium borohydride, sodium trimethoxy borohydride, potassium borohydride and lithium borohydride are employed. The described reaction is conveniently achieved by contacting the oxocaprylic acid with a suitable borohydride salt in the presence of a suitable solvent. Generally an excess of the borohydride salt is employed to attain optimum results. Examples of some solvents in which the reaction can be effected are aqueous alcohols such as methanol, ethanol and isopropanol and solvents such as tetrahydrofuran, dioxane, isopropylamine, pyridine and water. At ordinary temperatures the reaction proceeds to completion in from about 1 to 3 hours to form an intermediate metal complex.

An acid such as hydrochloric acid or sulfuric acid is added to decompose the metal complex and produce the desired 6,8-(hydrocarbon substituted mercapto)-S-hydroxycaprylic acid. Under acidic conditions, however, the resulting hydroxy acid cyclizes to the corresponding fi-lactone and ordinarily is isolated in this form. Alternatively, formation of the hydroxy acid structure is achieved by the addition of an alkaline agent sutficient to produce basic conditions. The presence of a base opens the o-lactone and yields the hydroxy acid as a salt which may be isolated if desired. Such products may be isolated byconventional techniques. Thus, the a-lactone is isolated by extraction of the acidic reaction mixture with an immiscible solvent such as chloroform and subsequent distillation.

The 6,8-(hydrocarbon substituted mercapto)-S-oxocaprylic acids which can be reduced in the described mannor may have hydrocarbon substituents Which are the same or difierent alkyl, alkenyl, alkynyl, aryl and aralkyl groups. This reduction, however, is more readily effected When such hydrocarbon substituents have 8 carbons or less, and in the synthesis of a-lipoic acid, it is preferred to utilize those compounds in which the hydrocarbon substituents are the same (bis) lower alkyl or alkenyl groups. Examples of compounds which are suitable for use in this reaction that might be mentioned are 6,8-bis (methylmercapto)-5-oxocaprylic acid, 6,8-bis(ethylmercapto)-5-oxocaprylic acid, 6,8-bis(propylmercapto)-5- oxocaprylic acid, 6,8-bis(butylmercapto)-5-oxocaprylic acid, 6,8-bis(phenylmercapto)-5-oxocaprylic acid, 6,8-bis (benzylmercapto)-5-oxocaprylic acid, 6,8-bis(allylmercapto)-5-oxocaprylic acid, 6,8-bis(2-methyl-l-ethyl-2-butenemercapto)-5-oxocaprylic acid, 6,8-bis(3-methyl-2- ethyI-Z-pentenemercapto) 5 oxocaprylic acid, 6,8-bis (propargylmercapto)-5-oxocaprylic acid, 6-ethyl-mercapto-8-propylmercapto-S-oxocaprylic acid and the like.

In a specific illustration of this reaction 6,8-bis (methylmercapto)-5-oxocaprylic acid may be reacted with so dium borohydride and the mixture acidified to obtain 6,8-bis(methylmercapto)-5-hydroxycaprylic acid 6-lactone. Other similar compounds which may be produced from the appropriate reactants by the application of these methods are 6,8-bis(methylmercapto)-5-l1ydroxycapryli-c acid, 6,8-bis(ethylmercapto)-5-hydroxycaprylic acid, 6,8-bis(propylmercapto)-5-hydroxycaprylic acid, 6,8-bis(butylmercapto)-5-hydroxycaprylic acid, 6,8-bis (phenylmercapto)-5-rydro-xycaprylic acid, 6,8-bis(benzylmercapto)-5-hydroxycaprylic acid, 6,8-bis(allylmercapto)-5-hydroxycaprylic acid, 6,8-bis(Z-methyl-l-ethyl- Z-butenemercapto)-5-hydroxycaprylic acid, 6,8-bis(3 methyl-2-ethyl-Z-pentenemercapto) 5 hydroxycaprylic acid, 6,8-bis(propargylmercapto)-5-hydroxycaprylic acid, 6-ethylrnercapto-8-propylmercapto 5 hydroxycapryli-c acid and the like and a-lactones thereof.

According to the second step in this process the 6,8- (hydrocarbon substituted mercapto)-5-hydroxycaprylic acid c-lactone is reduced to the corresponding 6,8-(hydrocarbon substituted mercapto) caprylic acid. This reaction is achieved with any suitable reducing agent and, for this purpose, phosphorous-iodine has been found to be particularly useful. The reaction is conveniently effected by contacting the reactants in an acidic medium such as aqueous acetic acid, or aqueous mineral acids such as hydrochloric andphosphoric acids. Elevated temperatures such as the reflux temperatures are ordinarily used to accelerate the reaction and'under such conditions, from two to 20 hours is required to complete, the reaction. After the reaction has been completed the unreacted iodine is reduced, as by the action of sodium bisulfite, and'the product isolated from the mixture by conventional procedures. Thus, the 6, 8- hydrocarbon substituted mercapto) caprylic acids may be extracted with chloroform, the organic solution extracted with aqueous sodium bicarbonate acidified, reextracted into chloroform and the solvent evaporated. The product can be purified by distillation.

Examples of some of the novel compounds which may be prepared according to this method from the corresponding a-lactones are 6,8-(hydrocarbon substituted mercapto) caprylic acids wherein the hydrocarbon substituents are the same or different alkyl, alkenyl, alkynyl, aryl and aralkyl groups such as the compounds 6,8-bis- (methylmercapto) caprylic acid, 6,8-bis(ethylmercapto) caprylic acid, 6,8-bis(propylmercapto) caprylic acid, 6,8- bis(butylmercapto caprylic acid, 6,8-bis(phe nyhnercapto) caprylic acid, 6,8-bis(benzylmercapto) caprylic acid, 6,8-bis(allylmercapto) caprylic acid, 6,8-bis(2- methyl-l-ethyl-2-butenemercapto) caprylic acid, 6,8 bis- (3 methyl-2-ethyl-2-pentenemercapto) caprylic acid, 6,8 bis(propargylrnercapto) caprylic acid, 6-ethylmercapto-8- propylmercapto caprylic acid and other similar compounds.

'Esters of the 6,8-(hydrocarbon substituted mercapto) caprylic acids are readily produced by reacting the caprylic acids with the appropriate alcohol in the presence of a suitable esterifying acid like mineral acids such as hydrochloric acid and sulfuric acid. This reaction is most conveniently effected at slightly elevated temperatures. Isolation of the esters is accomplished by the usual procedures such as evaporation of the solvents.

The 6,8-(hydrocarbon substituted mecapto) caprylic acids are also esterified by preparing the corresponding acyl halide and reacting it with an 'alkanol, aryl alcohol or aralkanol to produce the desired ester. The acyl halides used as intermediates in this process may be prepared by reacting a 6,8-(hydrocarbon substituted mercapto) caprylic acid with a suitable halogenating agent such as thionyl chloride, oxalyl chloride, phosphorus trichloride, phosphorous tribromide and the like in a conventional solvent or excess of the hologenating agent if liquid. The acyl halides thus produced are separated from the reaction mixture and esterified by contact with the appropriate alcohol to form the desired ester.

Some of the esters which are produced according to. these procedures are the methyl, ethyl, propyl, benzyl and, phenyl esters of the 6,8-(hydrocarbon substituted mercapto) caprylic acids previously disclosed herein.

In addition, salts of the 6,8-(hydrocarbon substituted mercapto) caprylic acids may also be produced by reacting the acid with an alkali metal or alkaline earth metal hydroxide, carbonate or bicarbonate. Some-salts which may be produced in this way are the sodium, potassium, lithium, calcium and magnesium salts of the 6,8- (hydrocarbon substituted mercapto) caprylic acids.

The last step of this process is directed to conversion of the 6,8-(hydrocarbon substituted mercapto) caprylic acids to the desired 6,8-dithioloctanoic acid. This conversion is conveniently achieved with suitable ether cleaving agents such as anhydrous or concentrated aqueous mineral acids such as sulfuric acid, hydrochloric acid,hydrobromic acid, hydroiodic acid, phosphoric acid and thiourea hydrohalides such as isothiouronium chloproduct.

ride and bromide. To effect the reaction the reactants are preferably combined and-heated at an elevated temperature up to about C. for l to 5 hours. The reaction mixture is then cooled, extracted with a water immiscible solvent such as chloroform and the solvent evaporated under reduced pressure to obtain the desired 6,8-dithioloctanoic acid.

According to a further-embodiment of the present invention the 6,8-bis(alkenyl or aralkyl substituted mercapto) caprylic acids are converted to 6,8-dithioloctanoic acid by hydrogenolysis with an alkali metal in liquid ammonia. This reaction may be illustratedas follows;

cmomornomncoon CH2CH2CH(CE2)4C OOH sru SR s11 srr III IV wherein R and R represent alkenyl and aralkyl groups.

The reaction is conveniently effected by adding the caprylic acid to liquid ammonia at about its boiling point and subsequently adding an alkali metal such as sodium, potassium or lithium to the resulting mixture. The re action goes to completion quickly to form the desired Excess alkali metal is neutralized by the addition ofammonium salts and the product is conveniently recovered by allowing the ammonia to boil off. It is purified by acidification and extraction with a suitable solvent such as chloroform. In specific illustrations of this process 6,8-bis(allylmercapto) caprylic acid and6,8-i bis(benzylmercapto) caprylic acid are, converted'to 6,8- dithioloctanoic acid by reaction with sodium in liquid ammonia.

According to another embodiment of the presentinvention there is provided S-hydroxy-S-[3-(1,2*dithiacyc1opentyl)] pentanoic acid which may be briefly called 5 hydroxy a-lipoic acid, and processes for preparing this andnovel intermediate compounds usefulin these processes.

It is now found that 5-hydroxy-5[3-(l,2-dithiacycl0- p entyl)] pentanoic acid and its fi-lactone is obtained by treating a 6,8-bis(alkenyl or aralkyl mercapto)-S-hydroxycaprylic acid or fi-lactone thereof (II) with an alkali metal in liquid ammonia to produce 5-hydroxy-6,8- dithioloctanoic acid or the 6-lactone thereof (V) and oxidizing said compound to produce the desired dithiacyclo compound (VI). This process may be illustrated, as follows in which the fi-lactones are employed as reactants and obtained in the process, but it is understood that the processis equally operable with' the hydroxy acids:

wherein R and R represent alkenyl and aralkyl groups.

The production of 5-hydroxy-6,8-dithioloctanoic acid and its a-lactone is effected by reacting a v6,8-bis(alkenyl or aralkyl mercapto)-5-hydroxycaprylic acidor its fi-lactone with an alkali metal in liquid ammonia.- The conditions suitable for achieving this reaction are substantially those which have been previously describedqin detail hereinabove in effecting a similar reaction. The product of the present reaction is a mixture of the. hydroxy acid and 5-lactone structures although under the conditions of reaction theflformationof a saltv of the i sure.

.fied and extracted with ether.

hydroxy acid is favored. Ordinarily, however, the product is isolated as'the 6-lactone by neutralizing the excess alkali metal, removing ammonia, taking the residue up in aqueous acid and extracting with ether. Examples of some compounds which may be converted to the 5- hydroxy-6,8-dithioloctanoic acid and fi-lactone thereof are 6,8-bis(allylmercapto)-5-hydroxycaprylic acid and 6,8- bis(benzylmercapto)-5-hydroxycaprylic acid and other similar compounds disclosed herein.

' Oxidation of 5-hydroxy-6,S-dithioloctanoic acid or the a-lactone thereof to S-hydroxy 5 [3-(1,2-dithiacyclopentyl)] pentanoic acid or the a-lactone thereof is conveniently accomplished by treatment with an oxidizing agent such as iodine-potassium iodide. This reaction is readily achieved in an inert solvent such as ether at ordinary temperatures. The reaction goes to completion in a short time. The reaction mixture is then treated in the usual ways to recover the product. Thus, the mixture may be treated with sodium bisulfite to reduce excess iodine, washed with water and evaporated under reduced pressure to remove the solvent. The product is ordinarily obtained as the a-lactone but under basic conditions the corresponding hydroxy acid may be obtained.

In the practice of this invention the 6,8-(hydrocarbon substituted mercapto)-5-oxocaprylic acids used as starting materials may be conveniently prepared according to processes disclosed by Wagner in U. S. patent application Serial No. 369,535, filed July 21, 1953, and by Holly, Wagner, Walton and Hoffman in U. S. patent application Serial No. 396,334, filed December 4, 1953, now U. S. Patent No. 2,809,978.

EXAMPLE 1 6,8-bis(methylmercapto)-5-hydr0xycaprylic acid -lactone About 8.5 g. of 6,8-bis(methylmercapto)-5-oxocaprylic acid is dissolved in 370 ml. of ethanol and 26 ml. of water is added. The solution is cooled in an ice bath and 6.7 g. of sodium borohydride is added portion-wise. After the initial vigorous reaction has subsided the mixture is allowed to stand at room temperature for two hours. The mixture is acidified to pH 3 with concentrated hydrochloric acid, filtered and the the filtrate adjusted to pH 8 with 8 N sodium hydroxide. After filtration the ethanol is removed by avaporation under reduced pres- 100 ml. of water is added, the pH is adjusted to 3 and the 6,8-bis(methylmercapto) 5 hydroxycaprylic acid fi-lactone is isolated by chloroform extraction. The chloroform solution is dried over anhydrous magnesium sulfate, filtered and evaporated to isolate the product. It is purified by distillation under reduced pressure at a pot temperature of 165l90 C. at pressures of 75-300 N =1.5384-1.5398; mol. weight (ebulliometric): 234:2 (calc. 234).

EXAMPLE 2 6,8-bis(ethylmercapt --hydr0xycapry lic acid fi-lactone Seven ml. of water and 100 ml. of ethanol are combined and 2.5 g. of 6,8-bis(ethylmercapto)-5-oxocaprylic acid is added to the mixture. The solution is cooled and 2 g. of sodium borohydride is added slowly with stirring. After the reaction is completed the mixture is acidified with sulfuric acid and the a-lactone of 6,8-bis(ethylmercapto)-5-hydroxycaprylic acid is thereby obtained. The mixture is filtered and concentrated under reduced pressure. The concentrate is diluted with water, acidi- The product is obtained by removing the solvent under diminished pressure.

6 EXAMPLE 3 6,8-bis(allylmercapt0)-5-lzydroxycapi'ylic acid fi-lactone Five g. of 6,8-bis(allylmercapto)-5-oxocaprylic acid is dissolved in 220 ml. of dioxane and 40 ml. of water and cooled. To the cooled solution is added about 4 g. of potassium borohydride at such a rate as to prevent overheating. After the vigorous reaction has subsided the mixture is warmed to room temperature and allowed to stand several hours. The mixture is acidified with hydrochloric acid, filtered, the pH adjusted to 7 concentrated and extracted with chloroform. The chloroform extract is concentrated under diminished pressure to remove the solvent. The 6,8-bis(allylmercapto)-5-hydroxycaprylic acid s-lactone is purified by distillation under reduced pressure.

EXAMPLE 4 6,8-bis(phenylmercapto)-5-hydroxycaprylic acid fi-lactone 8 g. of lithium borohydride is added slowly to a cooled solution of 10 g. of 6,8-bis(phenylmercapto)-5-oxocaprylic acid in 350 ml. of tetrahydrofuran and 50 ml. of water. The reaction is vigorous and cooling is maintained to prevent overheating. After completion of the reaction hydrochloric acid is added to pH 3. The mixture is filtered and concentrated under reduced pressure. After dilution with water the product is extracted with chloroform and the extract is concentrated under diminished pressure to give the fi-lactone of 6,8-bis(phenyl mercapto)-5-hydroxycaprylic acid.

EXAMPLE 5 6,8-bis(benzylmercapr0)-5-hydr0xycaprylic acid a-lactone Four g. of 6,8-bis(benzylmercapto)-5-oxocaprylic acid is dissolved in ml. of methanol and 10 ml.-of water. The mixture is cooled and 4 g. of sodium borohydride is added slowly in small portions. The mixture is warmed to room temperature and after several hours is acidified with sulfuric acid and filtered. The mixture, adjusted to pH 7, is concentrated under reduced pressure, diluted with water and extracted with ether. The ether is removed in vacuo and the 6,8-bis(benzylmercapto)-5-hydroxycaprylic acid 6-lactone is purified by distillation under reduced pressure.

EXAMPLE 6 6 methylmercapto 8 ethylmercapto 5 hydroxycaprylic acid 6-lact0ne To acooled solution of 7 g. of 6-methylrnercapto-8- ethylmercapto-S-oxocaprylic acid in 300 ml. of methanol and 75 ml. of water is added very slowly 6 gm. of sodium borohydride with stirring. Heat is evolved and cooling is continued until the reaction subsides. The mixture is allowed to warm to room temperature gradually and after several hours is acidified with hydrochloric acid to pH 2. The mixture is filtered, adjusted to pH 7 with sodium hydroxide and filtered. The filtrate is concentrated, diluted with water and acidified with hydrochloric acid. The product is extracted with ether and isolated by concentration under reduced pressure. The 6-methylrnercapto 8-ethylmercapto-S-hydroxycaprylic acid a-lactone is recovered as an oil.

' EXAMPLE 7 6,8-bis(methylmercapto)caprylic acid 1.36 g. of 6,8-bis(methylmercapto)-5-hydroxycaprylic acid fi-lactone is dissolved in 25 m1. of glacial acetic acid and 5 ml. of water. To this solution is added 540 mg. of red phosphorus and 2.21 g. of iodine. The mixture is refluxed for 17 hours, cooled, filtered and then diluted with. ml. of water. The excess iodine is reduced by the addition of aqueous sodium bisulfite and the solution is extracted with chloroform. Thechloroform extract is washed with saturated aqueous sodium chloride, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to yield 6,8-bis(methylmercapto) caprylic acid.

The methyl ester is prepared by reacting 6,8-bis (methylmercapto) caprylic acid with phosphorus trichloride to prepare the corresponding acyl chloride which upon reaction with methanol gives the desired methyl ester. The ethyl, propyl, benzyl and phenyl esters are prepared in a similar manner.

Salts of 6,8-bis(methylmercapto) caprylic acid are produced by reacting the acid with a base such as an alkali metal or alkaline earth metal hydroxide, bicarbonate or carbonate.

EXAMPLE 8 6,8-bis(ethylmercapto) caprylic acid About 0.5 g. of 6,8-bis(ethylmercapto)--hydroxycaprylic acid fi-lactone is added to 20 ml. of phosphoric acid (90%) and 3 ml. of water. After adding0.15 g. of red phosphorus and 1 g. of iodine the mixture is refluxed for hours. The mixture is cooled, sodium bisulfite added to reduce the iodine and the mixture isextracted with ether. The ether extract is concentrated to obtain 6,8-bis(ethylmercapto) caprylic acid. The product is further purified by bicarbonate extraction and by distillation under reduced pressure.

EXAMPLE 9 6,8-bis(allylmercapto) caprylic acid To a mixture of 10 ml. of glacial acetic acid and 1 ml. of water is added 0.45 g. of 6,8-bis(allylmercapto)-5- hydroxycaprylic acid fi-lactone. The mixture is cooled and 0.1 g. of red phosphorus and 0.5 g. of iodine is added. After refluxing for 6 hours the mixture iscooled, sodium bisulfite is added to reduce the iodineand the product is extracted with chloroform. The chloroform solution is extracted with saturated aqueous sodium bicarbonate and the acidic product is isolated by acidifying to pH 3 and extraction with chloroform. The 6,8- bis(allylmercapto) caprylic acid is isolated by evaporating the solvent.

Other compounds which are prepared by this process by reduction of the corresponding S-hydroxy precursors are 6,8-bis(benzylmercapto) caprylic acid, 6,8-bis(phenylmercapto) caprylic acid, 6-methylmercapto-8-ethylmercapto caprylic acid and 6-benzylmercapto-8-methylmercapto caprylic acid.

- EXAMPLE 10 6,8-dithioloctanoic acid from 6,8-bis(methylmercapto) caprylic acid About 314 mg. of 6,8-bis(methylmercapto) caprylic acid in -5 ml. of 50% aqueous sulfuric acid is heated at 85 C. for 3 /2 hours. The mixture is then poured into water and the 6,8-dithioloctanoic acid is extracted with chloroform and concentrated under reduced pressure to isolate the product.

Alpha lipoic acid is prepared from the 6,8-dithioloctanoic acid produced above by reacting it in chloroform with aqueous 10% iodine-potassium iodide. The excess iodine is reduced with aqueous sodium bisulfite, the chloroform extract is washed with water, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to isolate the product.

EXAMPLE 1-1- 6,8-dithioloctanic acid from 6,8-bis(allylmercapto) caprylic acid To 10 ml. ofconcentrated hydrochloric acidis added '1 gm. of 6,8-bis(allylmercapto) caprylic acid and the mixture heated at 50 C. for 10 hours. The-mixture is m ((3 cooled, added. to water and the 6,8-dithioloctanoic acid extracted with ether. The product is recovered-by evaporating the solvent.

EXAMPLE l2 6,8-diihi0l0ctan0ic acid from 6,8-bis(benzylmercapto) caprylic acid A concentrated aqueous solution (10 ml.) of phosphoric acid is warmed and to it is added 0.5 g. of 6,8- bis(benzylmercapto) caprylic acid. The mixture is heated to C. for '2 hours, cooled and water is added. Recovery of 6,8-dithioloctanoic acid is achieved by extraction with chloroform and concentration under reduced pressure.

EXAMPLE 13 6,8-dithi0l0ctan0ic acid by hydrogenolysis of 6,8-bis (allylmercapto) caprylic acid Into 100 ml. of liquid ammonia is placed 1 g. of 6,8- bis(allylmercapto) caprylic acid with stirring. Following solution about 1 g. of sodium is added in increments. Ammonium chloride is added to neutralize the excess sodium and the ammonia removedbyevaporation under reduced pressure. 50 ml. of water is added to the residue and enough concentrated hydrochloric acid added to reach pH 3. The 6,8-dithioloctanoic acid is extracted with chloroform and is isolated by evaporation of the solvent.

EXAMPLE 14 5-hydroxy-6,8-dithi0l0ctanoic acid-E-lactone About 1.2 g. of 6,8-bis(allylmercapto)-5-hydroxycaprylic acid is dissolved in 100 ml. of liquid ammonia and sodium is added in small portions until the blue color is permanent. The excess sodium is neutralized by the addition of ammonium sulfate to the mixture. The liquid ammonia is allowed to evaporate, the residue is taken up in 30 ml. of water and the solution is acidified to pH 3 with concentrated hydrochloric acid. The mixture is extracted with ether and the 5-hydroxy-6,S-dithioloctanoic acid-fi-lactone is isolated by evaporation of the solvent.

Itsinfrared spectrum in carbon tetrachloride solution shows a bonded hydroxyl group in the 3-4 region and a strong bond at 585 indicative of the carboxyl group. In addition, the absence of a band at 6.09 shows complete removal of the allylic groups.

EXAMPLE 15 5 -hydroxy-5 [3- (1 ,Z-dith iacyclopentyl) pentanoic acid-B-lactone The 5-hydroxy-6,S-dithioloctanoic acid-B-lactone produced as in Example 14 is taken up in ether and oxidized with aqueous 10% iodine-potassium iodide. Excess iodine is reduced with aqueous sodium bisulfite. The S-hydroxy-S[3-(1,2-dithiacyclopentyl)lpentanoic acid-6 lactone is isolated by evaporation of the solvent under diminished pressure. Its ultra-violet spectrum shows a shoulder at 273 mp (E%=12,6) and a plateau at 320 m (E% =5.4).

EXAMPLE 16 6,8-dithi0l0ctanoic acid by hydrogenolysis of 6,8-bis (benzylmercapto) caprylic acid To 100 ml. of liquid ammoniazis added 0.5 g. of 6,8- bis(benzylmercapto) caprylic acid with stirring. Metallic sodium is then added until a blue color persists. When a persistent blue color is obtained, ammonium chloride is added to neutralize the excess sodium and the ammonia is removed by evaporation under reduced pressure. 50 ml. of water is added to the residue plus sufficient hydrochloric acid to make the solution pH 3. The 6,8-dithioloctanoic acid is isolated by extraction into chloroformand removal of the organic solvent.

160 C. for one hour.

EXAMPLE 17 6,8-dithioloctanoic acid from 6,8-bis(methylmercapto) caprylic acid 133 mg. of 6,8 bis(methylmercapto) octanoic acid and 500 mg. of thiouronium chloride are mixed and heated at The mixture is cooled to room temperature and 3 ml. of 2.5 N NaOH is added. The solution is heated at 80 C. for ninety minutes. After being cooled to room temperature the mixture is acidified to pH 3 with concentrated hydrochloric acid and extracted with chloroform. The chloroform extract is evaporated to give 6,8-dithioloctanoic acid as a residue.

Various changes and modifications of the invention can be made and to the extent that such variations incorporate the spirit of this invention they are intended to be included within the scope of the appended claims.

What is claimed is:

1. A compound selected from the class consisting of compounds having the formula CH2CHzCHCH(CH2)3COOH SR SR and delta-lactones thereof, wherein R and R are selected from the class consisting of lower alkyl and lower alkenyl radicals having up to eight carbon atoms inclusive, benzyl and phenyl radicals.

2. The process which comprises treating a compound having the formula eight carbon atoms inclusive, benzyl and phenyl radicals. 3. The process which comprises treating a 6,8-bis 10 (loweralkylmercapto)-5-oxocaprylic acid with an alkali metal borohydride and acidifying the reduction mixture to produce the delta-lactone of a 6,8-bis (loweralkylmercapto) -5-hydroxycaprylic acid.

4. The process which comprises treating a 6,8-bis (allylmercapto)-5-ox0caprylic acid with an alkali metal borohydride and acidifying the reduction mixture to produce the delta-lactone of a 6,8-bis (allylmercapto)-5-hydroxycaprylic acid.

5. The process which comprises treating a 6,8-bis (loweralkenylmercapto)-5-oxocaprylic acid with an alkali metal borohydride and acidifying the reduction mixture to produce the delta-lactone of a 6,8-bis (loweralkenylmercapto)-5-hydroxycaprylic acid.

6. The process which comprises treating a 6,8-bis (methylmercapto)-5-oxocaprylic acid with an alkali metal borohydride and acidifying the reduction mixture to produce the delta-lactone of a 6,8-bis (methylmercapto)- 5-hydroxycaprylic acid.

7. The delta-lactone of 6,8-bis (loweralkylmercapto)- S-hydroxycaprylic acid.

8. The delta-lactone of 6,8-bis (loweralkenylmercapto)-5-hydroxycaprylic acid.

9. 6,8-bis (methylmercapto) 5 hydroxycaprylic acid delta-lactone.

10.6,8-bis (allylmercapto)-5-hydroxycaprylic acid delta-lactone.

11. 6,8-bis (benzylmercapto)-5-hydroxycaprylic acid delta-lactone.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,639 Lazier June 25, 1946 2,422,246 Lazier et al. June 17, 1947 2,493,071 Kendall Jan. 3, 1950 2,526,702 Smith Oct. 24, 1950 2,539,428 Jansen Jan. 30, 1951 2,576,901 de Jong Nov. 27, 1951 2,755,288 Bullock July 17, 1956 2,789,990 Bullock Apr. 23, 1957 OTHER REFERENCES Chaikin: I. A. C. S., 71: 122-125 (1949). Nystrom: J. A. C. S., 71: 3245-46 (1949). 

1. A COMPOUND SELECTED FROM THE CLASS CONSISTING OF COMPOUNDS HAVING THE FORMULA
 2. THE PROCESS WHICH COMPRISES TREATING A COMPOUND HAVING THE FORMULA 